The theme of this application is the comparative study of auditory processing of complex sounds. The comparative approach refers to the investigators' use of different techniques (anatomy, physiology, animals and human behavior/psychophysics, and modeling), different animal models (fish, chinchilla, and humans), and different hair cell systems refers to the auditory system's ability to determine the sources of sound. The auditory system's ability to use sound and vibration to determine the sources of sound, especially in multi-source acoustic environments, is a major cross-cutting theme of the proposal. Support if requested for five projects and two cores. Project 1 proposes to study [anatomically, physiologically (peripherally and centrally), and behaviorally] the mechanoreceptive lateral line system's ability to locate objects in the water field that flows past a fish. This research relies on past work on the lateral line system, the relatively well understood electroreceptive system, and auditory processing in fish. Project 2 covers work with fish on complex sound processing like that associated with stimuli that generate a complex pitch perception and sound localization. The research is based on both behavioral and physiological (peripheral and central) techniques. Project 3 continues research investigating binaural differences to determine and locate sound sources, especially when the interaural differences associated with those sources differ across the spectrum of the complex sound reaching the listener. Work on the cocktail party effect and echo processing are also proposed. Project 4 is a continuation of work on the use of slow coherent temporal modulation to aid the auditory system in sound source determination. In addition to human psychophysical experiments, the project includes animal psychophysical and physiological components investigating the responses of chinchillas to complex sounds with slow temporal modulations. Project 5 continues the study of the physiological basis for processing complex sounds with strong temporal regularities, such as exists in most stimuli which are perceived as having a pitch. A stimulation of particular interest is iterated rippled noise. This project involves human and animal psychophysics and auditory brainstem physiology. Core A requests support for the administrative and technical aspects of the Program Project and Core B requests support for the subjects (both human and animals) used in the five projects.